WPF - 依赖属性初始化

Question

我正在尝试实现一个将图像投影到 3D 模型上的 WPF 组件。为了使其使用起来更整洁，我尝试使用依赖属性，以便我可以通过以下方式从我的视图中绑定控件：

<viewers:MyViewer
    ProjectedImageSource="{Binding ViewModel.ProjectedSource}"
    Visibility="{Binding Path=HueMapVisible, Converter={StaticResource booleanToVisibilityConverter}}"
    />

控件如下：

<UserControl x:Class="ImageProjector.Controls.Viewers.MyViewer"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300">
    <LayoutGrid>
        <Viewport3D Name="Viewport" Grid.ColumnSpan="7" Grid.RowSpan="7" />
    </LayoutGrid>
</UserControl>

代码隐藏：

public interface IMyViewer { }

public partial class MyViewer : UserControl, IMyViewer
{
    private IImageModel3D imageModel3D;

    public MyViewer() : this(Ninjector.Get<IImageModel3D>()){ }

    public MyViewer(IImageModel3D imageModel3D)
    {
        this.InitializeComponent();

        this.ProjectedImageSource.Changed += ProjectedImageSource_Changed;
    }

    private void ProjectedImageSource_Changed(object sender, EventArgs e)
    {
        imageModel3D.SetImage((BitmapImage)sender);
    }

    public static readonly DependencyProperty ProjectedImageSourceProperty = DependencyProperty.Register(
                                                                    "ProjectedImageSource",
                                                                    typeof(BitmapSource),
                                                                    typeof(MyViewer));

    public BitmapSource ProjectedImageSource
    {
        get => (BitmapSource)this.GetValue(ProjectedImageSourceProperty);
        set => this.SetValue(ProjectedImageSourceProperty, value);
    }
}

我遇到的问题是，在构造函数中调用 ProjectedImageSource 时为 null（我也在 Loaded 回调中尝试过），因此我无法设置 Changed 事件处理程序。

我知道有一个 ValidateValue 回调，但这需要是一个静态静态，因此在这种情况下不起作用。

我可以使用一些技巧来使此功能正常工作，还是尝试这样做存在根本缺陷？

Answer 1

您应该使用依赖属性元数据注册一个 PropertyChangedCallback：

public static readonly DependencyProperty ProjectedImageSourceProperty =
    DependencyProperty.Register(
        nameof(ProjectedImageSource),
        typeof(BitmapSource),
        typeof(MyViewer),
        new PropertyMetadata(ProjectedImageSourceChanged));

private static void ProjectedImageSourceChanged(
    DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
    var viewer = (MyViewer)obj;

    viewer.imageModel3D.SetImage(e.NewValue as BitmapImage); // may not be a BitmapImage
}

或更短：

public static readonly DependencyProperty ProjectedImageSourceProperty =
    DependencyProperty.Register(
        nameof(ProjectedImageSource),
        typeof(BitmapSource),
        typeof(MyViewer),
        new PropertyMetadata(
            (o, e) => ((MyViewer)o).imageModel3D.SetImage(e.NewValue as BitmapImage)));

---

请注意，您的 IImageModel3D.SetImage 方法似乎不需要 BitmapImage 参数。最好改用BitmapSource，并像这样编写您的PropertyChangedCallback：

public static readonly DependencyProperty ProjectedImageSourceProperty =
    DependencyProperty.Register(
        nameof(ProjectedImageSource),
        typeof(BitmapSource),
        typeof(MyViewer),
        new PropertyMetadata(
            (o, e) => ((MyViewer)o).imageModel3D.SetImage((BitmapSource)e.NewValue)));

如果 SetImage 确实需要 BitmapImage，则应更改依赖属性的类型。